1. Field of the Invention
The present invention relates to a process for manufacturing a solid state electrolytic capacitor having a conductive polymer compound as a solid state electrolyte.
2. Description of the Related Art
According to a conventional method of manufacturing a solid state electrolytic capacitor, a sintered material with an anodized coating or etched foil is soaked in manganese nitrate solution and is then thermally decomposed, providing manganese dioxide as a solid state electrolyte. In this method, however, high heat and nitrogen gas caused in the thermal decomposition process will damage the anodized coating, so that the dielectric strength may drop and the leakage current may increase. Further, since manganese dioxide produced by this method is porous, the capacitor will have insufficient conductivity and a high-frequency characteristic inferior to that of a ceramic capacitor or a film capacitor.
As a solution to those shortcomings, a conductive polymer compound is used as a solid state electrolyte.
There are a chemical oxidative polymerization method and an electrolytic oxidative polymerization method to form a conductive polymer compound on a microporous anode.
A conductive polymer compound acquired by the chemical oxidative polymerization has a shortcoming that it has a lower conductivity and needs more time for its formation than one acquired by the electrolytic oxidative polymerization.
According to the electrolytic oxidative polymerization, however, since an anodized coating is made of an insulating material, it is difficult to be rendered conductive, thus impeding acquisition of a conductive polymer compound with a uniform and sufficient thickness.
To overcome these problems, there has been proposed a method of forming an electrolytically oxidative-polymerized film by forming a thin conductive polymer compound on an anodized coating by chemical oxidative polymerization, and contacting one of the electrodes for electrolytic oxidative polymerization with this polymer compound film.
This method of producing a solid state electrolytic capacitor requires that a needle-like electrode should contact each electrolytic capacitor element. Accordingly, this requires many steps, and may cause the anodized coating to be damaged.